Fan engine thrust monitor

ABSTRACT

A warning signal is generated if a high bypass ratio fan-type gas turbine engine fails to develop adequate thrust for takeoff of an aircraft. Two engine operating parameters are derived, referred compressor speed and referred fan speed. After a takeoff is initiated, a warning signal is developed under any one of three conditions: (1) if the referred compressor speed is less than a pre-established reference level; (2) if the referred fan speed is less than a pre-established reference level; and (3) if the ratio of compressor speed to fan speed is less than a preestablished reference level.

United States Patent 1 Hohenberg [451 June 5, 1973 541 FAN ENGINE THRUST MONITOR 3,678,742 7/1972 Westcottetal. ..73 117.3

751 tzRdolh Hhnb T bll, men or g o e rum u Primary Examiner-Kathleen H. Claffy Assistant ExaminerThomas L. Kundert [73] Assignee: Avco Corporation, Stratford, Conn. Attorney-Charles M. Hogan et al.

[22] Filed: Mar. 27, 1972 [57] ABSTRACT [21] Appl 238243 A warning signal is generated if a high bypass ratio fan-type gas turbine engine fails to develop adequate 52 s CL 73 17 T, 340 27 NA, 73 1 173 thrust for takeoff of an aircraft. Two engine operating 60/39 ()9R parameters are derived, referred compressor speed 51] Int. Cl. ..G0lm 15 00 and referred fan speed- After a takeoff is initiated, a [58] Field of Search ..340/27 R, 27 NA; warning Signal is develoPed under any 0f three 73/1173 1174 178 R 178 H 178 conditions: (1) if the referred compressor speed is less 60;39 28 14 5 than a pre-established reference level; (2) if the referred fan speed is less than a pre-established 56 R f reference level; and (3) if the ratio of compressor eerences Cled speed to fan speed is less than a pre-established UNITED STATES PATENTS reference level.

3,338,050 8/1967 Ferrel et al. ..73/l78 R 5 Claims, 2 Drawing Figures 'NLET f THROTTLE POSITION COMPRESSOR |6 SPEED COMPRESSOR LANDING GEAR POSITION l5 REFERRING COMPARATOR 44 COMPRESSOR r46 SPEED i AIR sENsoR COMPARATOR SPEED REE SENSOR $47 INLET 23 43 TEMPERATURE 27 SENSOR FAN SPEED FAN L REFERRING 2i; COMPARATOR AND 40 FAN SPEED 25 l SENSOR 28 REE TIME DELAY -39 22/ 30A 3| as SPEED RATIO RATIO COMPARATOR 30B 34\l I9 LOGIC CIRCUIT FEED BACK ELEMENT PATENTEUJUN 5 I975 SHEET 2 OF 2 s I Y so 4a eo SPEED PULSE SENSOR SHAPER 'NTEGRATOR a FAN ENGINE THRUST MONITOR BACKGROUND AND SUMMARY OF THE INVENTION During the taking off of any aircraft it is essential that the pilot knows whether he has adequate thrust. At the present time there are no known satisfactory methods for making a direct measurement of thrust. The present invention is useful in connection with a high bypass ratio fan-type gas turbine engine and it provides a sys tem for determining whether or not there is adequate thrust for takeoff, and for properly and promptly advising the pilot.

It is known that the referred compressor speed of the core engine is a measure of the power produced. It is also known that the referred fan speed of an engine is a measure of the conversion of the available mechanical power into thrust. In addition, it is known that the speed ratio between the compressor and the fan is a constant under takeoff conditions for a normally operating fan engine. This invention uses three comparators, a compressor speed comparator, a fan speed comparator, and a ratio comparator, each having predetermined reference points. Each of the comparators produces an output in binary form, the binary output being in one state when the input to the comparator is below the predetermined reference point, and in a second state when the input to the comparator is above the reference point. The output from each of the three comparators is applied to a logic circuit which is enabled by the simultaneous presence of three comparator outputs in one particular state, but only after the engine is in a take-off condition, as indicated simultaneously by throttle position, landing wheel position and air speed. The three comparator inputs to the logic circuit are sampled after a predetermined time delay. If all three comparators have an output indicating that the reference point has been exceeded, then conditions are proper for takeoff. On the other hand, if any of the outputs from the comparator do not indicate that the reference point has been exceeded, then there will be an indication that the takeoff attempt should be aborted, or that there is an instrument error.

THE DRAWINGS FIG. 1 is a block diagram of a fan engine thrust monitor made in accordance with this invention; and

FIG. 2 is a block diagram of a system for determining referred compressor and fan speeds.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, inlet temperature is sensed by means of a resistance thermometer, thermocouple or other temperature sensor positioned at the air inlet of the compressor of a gas turbine engine (not shown) while the actual compressor speed is sensed by means of a magnetic pickup 12 or other conventional speedsensing mechanism. The temperature sensor 10 provides a voltage output which is applied to one input terminal 13 of a compressor speed referring circuit 14. The output from the compressor speed sensor 12 consists of voltage pulses which are applied to the second input terminal of the referring circuit 14. The details of the referring circuit 14 are shown in FIG. 2 which will hereinafter be described in detail. The referring circuit converts the actual compressor speed to a voltage representing referred speed. The voltage output from the referring current 14 is applied to the first input terminal 16 of a comparator 17.

The second input 18 of compressor comparator 17 is provided with a predetermined reference voltage representing the referred compressor speed below which takeoff should not be attempted. The output from the comparator 17 is applied to the first input terminal 19 of a logic circuit 20.

Similarly the inlet temperature of the fan is sensed by means of a temperature sensor 21 positioned at the air inlet of the fan while the actual fan speed is sensed by means of a magnetic pickup 22 or other conventional speedsensing mechanism. The temperature sensor 21 provides a voltage output which is applied to one terminal 23 of a fan speed referring circuit 24. The output from the compressor speed sensor 22 consists of voltage pulses which are applied to the second input terminal 25 of the referring circuit 24. The details of the referring circuit 24 are identical with the details of the compressor speed referring circuit 14 and will be described in connection with Fig. 2. The referring circuit 24 converts the actual fan speed to a voltage representing referred fan speed. The voltage output from the referring circuit 24 is applied to the first input terminal 26 of a fan comparator 27.

The second input terminal 28 of fan comparator 27 is provided with a predetermined reference voltage representing the referred fan speed below which takeoff should not be attempted. The output from the comparator 27 is applied to the second input terminal 29 of the logic circuit 20.

The output from each of the speed sensors 12 and 22 is also applied to the first and second input terminals 30A and 30B of a speed ratio circuit 31. The speed ratio circuit develops a voltage output representing the ratio of actual compressor speed to actual fan speed and is applied to the first input terminal 32 of a ratio comparator 33. The second input terminal 34 of the ratio comparator 33 is supplied with a reference voltage representing the proper ratio of compressor and fan speeds for takeoff. The output of the comparator changes state when the ratio is not proper. The output from the ratio comparator 33 is applied to the third input terminal 34 of logic circuit 20. While this comparator is not essential to performance, it provides a system check which can indicate that an instrument error exists.

The three comparators 17, 27 and 33 are each twostate or binary devices, each having a first state output, for example, zero when the input voltage is below the reference voltage, and having a second state output, for example, one, when the input voltage exceeds the reference voltage.

When the logic circuit 20 is sampled, an output signal is generated at one of its three output terminals 36, 37 or 38, depending on the states of the signals at their input terminals 19, 29 and 34. The logic circuit is sampled only after the generation of a time delayed signal from a time delay network 39. The time delayed signal is developed only after receipt of an output signal from an AND gate 40. The AND gate 40 develops an output signal only when each of its input terminals 41, 42 and 43 have been supplied with a predetermined input signal. Terminal 41 must be provided with an input signal representing throttle position for takeoff. Terminal42 must be provided with an input signal indicating that the landing gear is in takeoff position. Input terminal 43 must be provided with an input signal indicating that t= inlet air temperature in "F. of the compressor or the aircraft air speed is below stall. fan.

The signal for aircraft speed is derived by means of l claim an air speed sensor 44 which provides a voltage signal 3. in a a ning ys m o u e it a high bypass ratio representing air speed to the first terminal 4 of a comfan-type engine during takeoff, a pilot warning system parator 4 6. The second terminal 47 of the comparator comprising: 436 is provided with a reference voltage representing means for generating a first speed signal proportional stall speed. The comparator 46 provides an output voltto the referred compressor speed of said engine; age only when the input signal at terminal 45 is less a first reference source having a predetermined first than the reference voltage applied at terminal 47. 0 reference level;

When conditions for takeoff are met, that is when the means when Said first Speed signal is above said level throttle and landing gear positions are correct and for generating a first logic Signal; when the air speed is below stall, the output from the means for generating a o d p ed Signal proportime delay circuit provides a period to permit the entiol'lal t0 the referred fan Speed Of Said g gine to accelerate to takeoff speed (typically three to a secon reference source having a predetermined 5 seconds). At the end of the delay period, the logic cirsecond reference level; cuit is sampled and one of three logic outputs is genmeans when said first speed signal is above said level erated: (1) go; (2) abort takeoff: (3) instrument error. for generating a second logic signal; The relation between comparator signal and logic ciran initially disabled logic circuit, when enabled said cuit output after the predetermined time delay is as fol- 20 logic circuit developing a warning signal in the ablows: sence of either of said first and second logic signals;

Logic output Comparator output signal G0. Abort... Abort-.. Abort-.. Erlor Error Error Error. Compressorreferredspeed exeeedsrefereneelevel Yes No No Yes No Yes t N0 Yes. Fanreferredspeedexeeedsrefereneelevel Yes No N0 N0 Yes"... No Yes Yes. Compressorfanspeedisatrefereneelevel Yes No Yes. No Yes Yes No No.

Each of the outputs from the logic circuit 20 may be and used to activate warning lights in front of the aircraft means for enabling said logic circuit after a predeterpilot or may be used to activate other aircraft alarm or mined time period. monitoring systems. 2. The invention as defined in claim 1 wherein said The referring eil'euits e 24 are identical e are means for enabling said logic circuit comprises the out- Show bleck fhagram qp g put of a time delay circuit; and an AND gate initiated whether the circuit of FIG. 2 1s being used for referring i response to h Simultaneous li i f a p leompressor of fan Speed, the temperature sensor T and ity of condition responsive signals, the output of said I the Speed sensor 5 represent the elements 10 and 12, AND gate initiating the operation of said time delay or 21 and 22. The output from the speed sensor S is apcircuit plied to a preamplifier 48 which develops a series of 3 The invention as d fi d in claim 1, and

( Pulses having a Pulse repetition rate P P means for generating a third speed signal proportlonal to the speed of the compressor or fan as the case tional to compressor speed.

may be. The voltage pulses will be irregularly shaped means for generating a fourth Speed Signal propob and may vary in magnitude and pulse width. For that tional to fan speed;

reason they l apphed to Pulse shape. wh'ch means for generating athird logic signal proportional seljves to Pmv'de a Pulse W a cement with and to the ratio of said third speed signal to said fourth height but whose duty cycle IS a function of pulse repe speed signal.

g i g g h h F P phtlse a third reference source having a predetermined rom t e pu se s aper is integrate in an lntegra or third reference level;

My pnlwlde i a h hg P2 means when said third logic signal deviates from said P mm P m a l P e mm 6 e third reference level for generating a third logic siggrator 60 IS applied to an isolation amplifier 62 which nal, said third logic signal being applied to said has a feedback impedance element 64 connected from logic circuit to modify said warning signal. its output to its input circuit. The feedback element is 4. The invention as defined in claim 3 wherein said vaned as a fhhchoh of the Output of the temperature means for enabling said logic circuit comprises the outsensor T.

The referring circuit serves to provide an output sigg z ggz gg ifig z sfigfikzfig sgpfigg i g. 2 :53:? l hhl at M output termlhal 68 which propomoha to ity of condition responsive slgnals, the output of said K X (Actual Speed)/ VF AND gate initiating the operation of said time delay where circuit 5. The invention as defined in claim 4 wherein said K is a proportionality C nst n condition responsive signals comprise a signal respon- Actual Speed is the rate of speed of the compressor sive to throttle position, a signal responsive to landing or fan, as the case may be; gear position and a signal responsive to air speed.

t9=(460+t)/519 and 65 a a s: it 

1. In a warning system for use with a high bypass ratio fan-type engine during takeoff, a pilot warning system comprising: means for generating a first speed signal proportional to the referred compressor speed of said engine; a first reference source having a predetermined first reference level; means when said first speed signal is above said level for generating a first logic signal; means for generating a second speed signal proportional to the referred fan speed of said engine; a second reference source having a predetermined second reference level; means when said first speed signal is above said level for generating a second logic signal; an initially disabled logic circuit, when enabled said logic circuit developing a warning signal in the absence of either of said first and second logic signals; and means for enabling said logic circuit after a predetermined time period.
 2. The invention as defined in claim 1 wherein said means for enabling said logic circuit comprises the output of a time delay circuit; and an AND gate initiated in response to the simultaneous application of a plurality of condition responsive signals, the output of said AND gate initiating the operatIon of said time delay circuit.
 3. The invention as defined in claim 1, and means for generating a third speed signal proportional to compressor speed; means for generating a fourth speed signal proportional to fan speed; means for generating a third logic signal proportional to the ratio of said third speed signal to said fourth speed signal; a third reference source having a predetermined third reference level; means when said third logic signal deviates from said third reference level for generating a third logic signal, said third logic signal being applied to said logic circuit to modify said warning signal.
 4. The invention as defined in claim 3 wherein said means for enabling said logic circuit comprises the output of a time delay circuit; and an AND gate initiated in response to the simultaneous application of a plurality of condition responsive signals, the output of said AND gate initiating the operation of said time delay circuit.
 5. The invention as defined in claim 4 wherein said condition responsive signals comprise a signal responsive to throttle position, a signal responsive to landing gear position and a signal responsive to air speed. 